Alkylthioalkyl lactones

ABSTRACT

Compounds of the formula ##STR1## and their preparation wherein R 1  and R 2  are each selected from H and alkyl wherein the alkyl moieties are straight or branched chain of 1-20 carbons, preferably 1-6 carbons. Readily prepared therefrom are the corresponding unsaturated esters of the formula R 2  S(R 1 )CH--CH 2  --CH═CH--COO-alkyl which are useful as intermediates in the preparation of herbicides.

This invention concerns novel alkylthioalkyl lactones and a markedlyimproved process for their preparation. The lactones find utility asintermediates in the preparation of herbicides.

The invention more particularly concerns the novel lactone compounds ofthe formula ##STR2## and their preparation wherein R¹ and R² are eachselected from H and alkyl wherein the alkyl moieties are straight orbranched chain of 1-20 carbons, preferably 1-6 carbons such as methyl,ethyl, propyl, isobutyl, or hexyl. Readily prepared from these lactonesare the corresponding unsaturated esters of the formula R² S(R¹)CH--CH₂--CH═CH--COO--alkyl which are useful as intermediates in the preparationof herbicides according to and such as those disclosed in U.K. Pat. No.2,090,246, incorporated herein by reference.

The present lactones are prepared by contacting an aldehyde of theformula ##STR3## with ketene at a temperature of from about 0° C. toabout 30° C., preferably from about 15° C. to about 25° C., in thepresence of a catalytic amount of a Lewis acid catalyst in a low-boilingether or ester solvent.

In a specific preferred embodiment, the present invention encompassesthe compound (I) of the formula ##STR4## and its manufacture, whichcompound is employed in the preparation of the herbicide of the formula##STR5## sold under the tradename SELECTONE. This herbicide is prepared,for example, from the above compound (I) by the reaction sequence##STR6##

In accordance with the present invention, ketene is reacted with thealdehyde at about 0° C. to about 30° C. in the presence of a catalyticamount (about 0.35 to about 35 mole % of the total moles of thealdehyde) of a Lewis acid catalyst such as BF₃, BF₃.Et₂ O, ZnBr₂, ZnI₂,FeCl₃, MgBr₂, or the like, in a low-boiling ether or ester solvent suchas diethyl ether, tetrahydrofuran, 1,4-dioxane, dipropyl ether, dibutylether, ethyl acetate, methyl acetate, dimethoxyethane or the like,according to the equation

The following examples will further illustrate the invention.

EXAMPLE 1 Preparation of Compound (I)

A solution of 38.6 g (0.288 mole) of distilled3-(ethylthio)butyraldehyde and 1.5 ml of BF₃.Et₂ O (0.01 moles) in 350cc of diethyl ether in a round bottom flask equipped with stirrer wasstirred at 20° C. on a water bath while ketene gas was added through afrit at such quantity and flow rate as to provide a controlled reaction.After about 1.5 hours, IR analysis of an aliquot showed all aldehyde tobe consumed and a strong β-lactone carbonyl band at 5.5μ. The mixturewas purged with N₂, washed with 25 ml of saturated aqueous NaHCO₃, driedwith MgSO₄, stripped of ether, and distilled (Kugelrohr 75°-85°/1 mm Hg)to give 36.0 g (72%) of β-lactone as a clear liquid. Mass spectrum andelemental analysis confirmed the Compound (I) structure.

EXAMPLE 2 Preparation of Intermediate Compound (II) of the Structure##STR8##

To a solution of 10.0 g (0.0575 mol) of Compound I in 50 ml of methanolin a round bottom flask equipped with stirrer was added 3.19 g (0.0590mol) of sodium methoxide and the mixture stirred overnight at ambienttemperature. The mixture was stripped of methanol and partitionedbetween ether and water. The organic phase was dried with MgSO₄ andstripped of solvent to give 8.4 g (71.2%) of crude β-hydroxy esteridentified by mass spectrum analysis (clear syrup).

A solution of 8.4 g (0.0407 mol) of this crude alcohol in 100 ml of drypyridine was treated at 20° C. with 7.98 g (0.0420 mol) ofp-toluenesulfonyl chloride and the mixture stirred at room temperaturefor 2.5 hours. The reaction mixture was then heated on the steam bath toabout 70° C. for 3 hours and let stand at room temperature overnight.The reaction mixture was poured into water, extracted with ethylacetate, washed with 10% HCl and then with water, dried with MgSO₄ andstripped of ethyl acetate. The residue was distilled in a short-pathapparatus to give 5.03 g (65.6%) of the desired Compound (II) identifiedby mass spectrum analysis.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications will be effected within the spirit and scope of theinvention.

I claim:
 1. A compound of the formula ##STR9## wherein R¹ and R² areeach selected from H and alkyl of 1-20 carbons.
 2. A compound accordingto claim 1 wherein R¹ and R² are each selected from alkyl of 1-6carbons.
 3. The compound according to claim 1 of the formula ##STR10##